AIR FILTRATION SYSTEM BALANCING MANUAL - …

1 800-500-9777 1 FAX 402-245-5196 AIR FILTRATION SYSTEM BALANCING MANUAL 312 SOUTH HWY. 73, PO BOX 398 FALLS CITY, NE 68355-0398 800-500-9777 Revision date 06/05/2008 800-500-9777 2 FAX 402-245-5196 Index SYSTEM SYSTEM Basic SYSTEM Component Dust Collecting Hoods & Air Flow Control Duct Dust 800-500-9777 3 FAX 402-245-5196 Introduction The information presented in this MANUAL is intended to familiarize operating personnel with the fundamentals of dust collecting systems, operation and proper BALANCING to assure maximum operating efficiency.

2 A dust collecting SYSTEM comprises a number of components, each of which must function in accordance with the original design criteria to assure maximum efficiency. A malfunction in any one part may cause the entire SYSTEM to become inoperable. The following instructions will detail these parts, describing their function in the SYSTEM and the procedure to use to ensure efficient operation. The original design data and drawings prepared when the systems were installed should be available for reference. It is recommended that you study these to become familiar with the arrangement of duct work, hoods and other equipment. The SYSTEM will have been balanced after the original installation was completed and a section of this MANUAL will describe BALANCING . It is imperative that you become familiar with this procedure and have the tools on hand to rebalance should it become necessary. Read over all the instruction manuals to become thoroughly familiar with each piece of equipment and keep recommended spare parts in stock.

3 800-500-9777 4 FAX 402-245-5196 SYSTEM Components A typical SYSTEM will normally consist of the following major items: Dust Collecting Hoods & Air Flow Control Gates. These are installed at dust producing areas and serve to confine the outflow of dust. Duct Work. The ductwork collects the dust from a number of hoods and is sized to ensure proper carrying velocity. SYSTEM Fan. The fan creates the vacuum necessary within the ductwork and hoods, which cause air to flow inward through the hood, carrying dust particles with it. Dust Collector. This term generally refers to cloth or cartridge filters that separate the dust from the air stream, allowing the clean air to dissipate to the atmosphere while confining the dust to a single discharge point. Rotary Valves. These serve as airlocks under the dust collectors to discharge collected dust and to minimize air flow either into or out of the collector depending on whether the SYSTEM fan is on the dirty or clean air side.

4 800-500-9777 5 FAX 402-245-5196 SYSTEM Terminology Manometer. A Manometer is an instrument used to measure pressure. It consists of a clear U tube with a graduated scale between the two legs, calibrated in inches. The zero point on the scale is at the mid-point between the top and the bottom. In use, the manometer is filled with water so that the level in each leg is at the zero point. The pressure reading obtained is the difference between the two levels. The difference is expressed as inches of water column, or WC. As an example, if the water rises in the leg connected to the hood, it will drop from the zero point on the leg that is open to the atmosphere, resulting in a total reading of 3 WC. Each manometer is equipped with two rubber hoses, which can be of any length, usually 6 to 8 long each.

5 However, in measuring static pressure, only one hose is normally used. Today, electronic manometers are widely available. Velocity Pressure (Pv). Velocity Pressure is the difference between total pressure and static pressure, and is used to calculate both FPM and CFM (refer to Basic Calculations on page 7). Velocity pressure is measured through the use of a Pitot tube in conjunction with a manometer. A velocity pressure of 1 WC to WC is considered normal, equivalent to about 4,000 to 5,000 feet per minute (FPM). Static Pressure (Ps). Static pressure is measured in inches of water with a manometer, which is described word pressure is always used even though in most cases we are talking about a dust control SYSTEM under a vacuum. This is the effect created by atmospheric pressure due to movement of air created by a fan. Your vacuum cleaner is a good example of this function. The fan does not suck dust off the floor, it creates a vacuum inside the nozzle (or hood), which causes outside air to flow into the nozzle at such a velocity that it picks up and carries dust particles along with it.

6 Total Pressure (Pt). Total Pressure is the combination of static and velocity pressures, and is expressed in the same units. It is an important and useful concept to use because it is easy to determine and, although velocity pressure is not easy to measure directly, it can be determined easily by subtracting static pressure from total pressure. This subtraction need not be done mathematically. It can be done automatically in the manometer. Pitot Tube. A Pitot tube is an instrument constructed as a tube within a tube. The inner tube is used to measure total pressure, and openings in the outer tube allow measurement of static pressure. Feet Per Minute (FPM). Term used to indicate the velocity of air in a duct. A velocity pressure of 1 WC, as measured with a Pitot tube, results in a velocity of approximately 4,000 FPM, which is usually sufficient to keep most dust in suspension in the duct. Cubic Feet Per Minute (CFM).

7 A term used to indicate the air volume from an individual hood or being handled by the filter or fan. As an example, a fan may be selected to handle 10,000 cfm at 10 static pressure. The 10,000 CFM is the total air to be handled by all hoods combined and the 10 static pressure is that required to provide the desired airflow at the furthest hood. 012312301231233" PsSIMPLE MANOMETERPsPsPtAIR FLOWPITOT TUBEPsPtFLOWPsPtPv 800-500-9777 6 FAX 402-245-5196 Anemometer. An instrument for measuring air velocity, used in SYSTEM BALANCING to measure face velocity for comparison to SYSTEM design specifications. Face Velocity. Air velocity measured with an anemometer at the air inlet or exhaust. Face velocity is expressed in feet per minute. Air to Cloth Ratio. A term indicating the ratio of the total amount of air in a filter divided by the total cloth area.

8 10,000 CFM in a filter having 1,000 square feet of cloth gives a ratio of 10 to 1. Magnehelic Gauge. An instrument usually furnished with a filter that provides a means of constantly monitoring the operating static pressure drop, or differential pressure (DP) across the filter bags and indicates if the filter is operating normally. A range of 0-10 WC is adequate on the dial. An increase above the desired pressure drop allowed for in the SYSTEM design would result in decreased airflow and a resultant decrease in the efficiency of the entire SYSTEM . Cross Sectional Area. The area of the cross section of an air duct, usually expressed in square feet. Cross sectional area is used in calculating CFM. Traverse Readings. Traverse readings are taken in the interest of accuracy, since the velocity of the air stream is not uniform across the cross section of a duct. Friction slows the air moving close to the walls, so the velocity is greater in the center of the duct.

9 To obtain the average total velocity in ducts of 4 diameter or larger, a series of velocity pressure readings must be taken at points of equal area. It is recommended that at least 20 readings be taken along two diameters In round ducts. In rectangular ducts, a minimum of 16 and a maximum of 64 readings are taken at centers of equal rectangular areas. The velocities are then averaged. These precautions should be observed for best accuracy: 1. Duct diameter should be at least 30 times the diameter of the Pitot tube. 2. Locate the Pitot tube in a duct section providing 8 or more duct diameters upstream and 5 or more diameters down stream of the Pitot tube. This length of duct should be free of elbows, size changes or obstructions. 3. Provide an egg-crate type of flow straightener 5 duct diameters upstream of Pitot tube. 4. Make a complete, accurate traverse. In small ducts or where traverse operations are otherwise impossible, a fairly good degree of accuracy can be achieved by placing the Pitot tube in the center of the duct.

10 Determine velocity from the reading and multiply by for an approximate average. R .316 RPITOT TUBE PLACEMENTSAT CENTERS OF EQUALCONCENTRIC AREASTRAVERSE ON ROUNDDUCT AREAPITOT TUBE PLACEMENTS ATCENTERS OF EQUALRECTANGULAR AREASTRAVERSE ON RECTANGULARDUCT AREAHot-wire and wind-vane anemometers 800-500-9777 7 FAX 402-245-5196 Basic Calculations Velocity Pressure (Pv) = Total Pressure (Pt) - Static Pressure (Ps)Pv = Pt - PsFeet Per Minute (FPM) = The square root of the Velocity Pressure (Pv) x = PvSq. Ft. of Cross Sectional Area (CSA) = ( ) x Duct Radius (R) 144 *CSA = R /144 Cubic Feet per Minute (CFM) = Cross Sectional Area x Feet Per Minute (FPM)CFM = CSA x FPM*Divide by 144 when duct radius is measured in inches. 800-500-9777 8 FAX 402-245-5196 FIELD TEST SHEETFAN OWNERFAN NAMEPLATE DATADATE BYFAN RPM APPX BHPMOTOR NAMEPLATE DATASKETCH OF INSTALLATIONSHOWING POINTS OF READINGREADINGSSP(OUTLET)SP(OUTLET)V PV PTOTALAVERAGEXXXXX 1 2 3 4 5 6 7 8 91011121314151617181920 PROBE POINTS IN A RECTANGULAR DUCTL/8L/4L/4L/4L/8W/8W/4W/4W/4W/8 LWR PROBE POINTS IN A ROUND =.